Ch. 3 - Evolution, Biodiversity, and Population Ecology: • Natural selection • How evolution influences biodiversity • Reasons for species extinction • Ecological organization • Population characteristics • Population ecology

Central Case Study: Striking Gold in a Costa Rican Cloud Forest • Golden toads were discovered in Monteverde, Costa Rica in 1964 – 200 males in a 16-ft. area

• The mountainous cloud forest was ideal for amphibians • The toads vanished from Earth within 25 years – Climate change caused the forest to dry out – A fungus also killed them © 2012 Pearson Education, Inc.

Evolution is the wellspring of biodiversity

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Natural selection

• Species: a population or group of populations … – Whose members share characteristics and …. – Can breed with each other to produce fertile offspring

• Population: a group of individuals of a species that live in the same area • Evolution: means change over time – Biological evolution: genetic change in populations over time

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• Evolution may be random – Or directed by natural selection

• Natural selection: The process whereby inherited characteristics that enhance survival and reproduction … © 2012 Pearson Education, Inc.

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Species adapt to the environment

Natural selection leads to biodiversity

• A parent that produces more offspring passes on more genes to future generations • Over time, characteristics (traits) that lead to better reproductive success become more prevalent • Adaptive trait (adaptation): a trait that promotes reproductive success • Sexual reproduction also leads to genetic variation

• Natural selection weeds out unfit individuals

– Producing new combinations of genes

• It also helps elaborate and diversify traits

• Environmental conditions determine the pressures of natural selection

– Which leads to the formation of new species

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Evidence of natural selection is everywhere

Evolution generates biological diversity

• It is evident in every adaptation of every organism • Artificial selection: the process of selection conducted under human direction

• Biological diversity (biodiversity): the variety of life across all levels of biological organization

– Producing the great diversity of dog breeds and crops

– – – –

Species Genes Populations Communities

• Scientists have described 1.8 million species – Up to 100 million species may exist – Tropical rainforests are rich in biodiversity

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Speciation produces new types of organisms • The process of generating new species from a single species • Allopatric speciation: species form as a result of physical separation of populations

Speciation results in diverse life forms • How do major groups diverge over time? • Phylogenetic trees: branching diagrams show relationships among species, groups, genes, etc. – Represent life’s history

– The main mode of speciation – Populations can be separated by glaciers, rivers, mountains – Each population, with its own set of mutations, diverges

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Fossils also show life’s history • Fossil: an imprint in stone of a dead organism • Fossil record: the cumulative body of fossils worldwide • Phylogenetic trees and the fossil record show: – – – –

Life has existed on Earth for 3.5 billion years Life evolved complex structures from simple ones Life evolved large sizes from small ones But natural selection can also favor simplicity and small size

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Extinction • Most species that once lived are now gone • Extinction: the disappearance of a species from Earth – Species last 1–10 million years

• Biological diversity is now being lost at an astounding rate – This loss of species is irreversible

Number of species = speciation – extinction © 2012 Pearson Education, Inc.

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Some species are vulnerable to extinction

Earth has had several mass extinctions

• Extinction occurs when the environment changes rapidly

• Background extinction rate: extinction usually occurs slowly, one species at a time • Mass extinction events: killed off massive numbers of species at once

– Natural selection can’t keep up, so species can’t adapt

• Many factors cause extinction: – Climate change, changing sea levels, severe weather – Arrival of new species, small populations – Specialized species

• Endemic species: exists only in a certain, specialized area – Very susceptible to extinction – These species usually have small populations © 2012 Pearson Education, Inc.

– Occurred five times in Earth’s history – 50–95% of all species went extinct at one time

• Cretaceous-Tertiary (K-T) event: 65 million years ago – A gigantic asteroid caused dinosaur extinction

• End-Permian event: 250 million years ago – 75–95% of species went extinct from unknown causes © 2012 Pearson Education, Inc.

We study ecology at several levels

Levels of ecological studies

• Ecology: studies interactions among organisms

• Population ecology: investigates population changes

– And their environment

• Biosphere: the total living things on Earth – And the areas they inhabit

– The distribution and abundance of individuals – Why some populations increase and others decrease

• Community ecology: focuses on patterns of species diversity and interactions • Ecosystem ecology studies living and nonliving components of systems to reveal patterns – Nutrient and energy flows

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Each organism has habitat needs

The niche: a multidimensional concept

• Habitat: the environment where an organism lives

• Niche: an organism’s use of resources

– It includes living and nonliving elements

• Habitat use: nonrandom patterns where organisms live • Habitat selection: the process by which organisms actively select habitats in which to live • Species use different criteria to select habitat – Soil, topography, vegetation, other species

• Species have different habitat needs – Depending on body size, season, etc.

• Species survival depends on having suitable habitats © 2012 Pearson Education, Inc.

Population size

– Along with its functional role in a community – Habitat use, food selection, role in energy and matter flow, interactions with other individuals

• Specialists: have narrow niches and specific needs – Extremely good at what they do – But vulnerable when conditions change

• Generalists: species with broad niches – They use a wide array of habitats and resources – Survive in many different places © 2012 Pearson Education, Inc.

Population density

All populations show characteristics that affect their future dynamics

• Population density: the number of individuals in a population per unit area • Large organisms usually have low densities – They need many resources and a large area to survive

• High densities make it easier to find mates

Humans drove passenger pigeons, North America’s most abundant bird, to extinction

• Population size: the number of individuals present at a given time – Can increase, decrease, cycle, or remain the same

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– But increase competition and vulnerability to predation – Also increase transmission of diseases

• Low densities make it harder to find mates – But individuals enjoy more space and resources

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Population distribution

Four factors of population growth or decline

• Population distribution (dispersion): spatial arrangement of organisms • Random: haphazardly located individuals, with no pattern

• Natality: births within the population • Mortality: deaths within the population • Immigration: arrival of individuals from outside the population

– Resources are widespread

• Uniform: evenly spaced individuals – Territoriality, competition

– Births and immigration add individuals to a population

• Emigration: departure of individuals from the population – Deaths and emigration remove individuals

• Clumped: most common in nature – Arranged according to resources © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc.

Population growth rate

Exponential population growth

• Growth rate: rate of change in a population’s size per unit time

• Exponential growth: a population increases by a fixed percent

– Equals (birth rate + immigration rate) – (death rate + emigration rate) – Tells us the net changes in a population’s size per 1000 individuals per year

• Growth rate is expressed as a percent: – Population growth rate * 100% – Populations of different sizes can be compared

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– Graphed as a J-shaped curve

• It occurs in nature with: – Small populations – Low competition – Ideal conditions

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Limiting factors restrain population growth

Carrying capacity

• Exponential growth rarely lasts • Limiting factors: physical, chemical, and biological attributes of the environment limiting population growth • Environmental resistance: all limiting factors together

• Carrying capacity: the maximum population size the environment can sustain

– Stabilizes the population size at its carrying capacity – Terrestrial animals: space, food, water, mates, shelter, breeding sites, temperature, disease, predators – Plants: sunlight, moisture, soil chemistry – Aquatic systems: salinity, sunlight, temperature, etc.

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Population density affects limiting factors

– Determined by limiting factors

• Limiting factors slow and stop exponential growth – Forms an S-shaped logistic growth curve © 2012 Pearson Education, Inc.

Perfect logistic curves aren’t often found

• Density-dependent factors: limiting factors whose influence is affected by population density – Increased density increases the risk of predation, competition for mates, and disease – Results in the logistic growth curve – Environmental resistance has a stronger effect on larger populations

• Density-independent factors: limiting factors whose influence is not affected by population density – Temperature extremes, floods, fires, and landslides

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Reproductive strategies vary among species

Population changes affect communities

• Biotic potential: an organism’s capacity to produce offspring • K-selected species: species with long gestation periods and few offspring (i.e., a low biotic potential)

• Scientists have noticed troubling changes in the environment • As Monteverde dried out, species have disappeared

– Offspring have a high likelihood of survival – The population stabilizes at or near carrying capacity – Good competitors

• r-selected species: species that reproduce quickly – Have a high biotic potential – Little parental care, populations fluctuate greatly

– Golden toads, harlequin frogs, and more had been pushed from their cloud-forest habitat into extinction – Species from lower, drier habitats moved into the cloud forest – Population sizes of cloud-forest bird species declined

• Changing climate and disease are causing population fluctuations and changing the makeup of communities

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© 2012 Pearson Education, Inc.

Conserving biodiversity

Costa Rica’s protection is paying off

• Human development, resource use, and population pressure are changing populations and communities • Factors threatening biodiversity have complex social, economic, and political roots

• Costa Rica was losing forests at the world’s fastest rate – Now, 25% of its area is under protection

• Ecotourism: tourists visit protected areas

– We must understand these factors to solve problems

• Millions of people are working to protect biodiversity and to safeguard ecological and evolutionary processes

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Ecotourism provides thousands of jobs and billions of dollars to Costa Rica’s economy

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Conclusion

Ch. 3 Written Assignment

• The fundamentals of evolution and population ecology are integral to environmental science • Natural selection, speciation, and extinction help determine Earth’s biodiversity • Understanding how ecological processes function at the population level is crucial to protecting biodiversity

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• You are a population ecologist studying animals in a national park, and policymakers are asking for advice on how to apportion the government’s limited conservation funds. How would you rate the following three species, from most vulnerable (and thus most in need of conservation attention) to least vulnerable? Give reasons for your choices. – A bird with an even (1:1) sex ratio that is a habitat generalist – A salamander endemic to the park that lives in high elevation forest – A fish that specializes on a few types of invertebrate prey and has a large population size

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